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1# Encoding and Decoding with an RSA Private Key (C/C++)
2
3<!--Kit: Crypto Architecture Kit-->
4<!--Subsystem: Security-->
5<!--Owner: @zxz--3-->
6<!--Designer: @lanming-->
7<!--Tester: @PAFT-->
8<!--Adviser: @zengyawen-->
9
10**Encoding**
11
121. Call [OH_CryptoAsymKeyGenerator_Create](../../reference/apis-crypto-architecture-kit/capi-crypto-asym-key-h.md#oh_cryptoasymkeygenerator_create) and [OH_CryptoAsymKeyGenerator_Generate](../../reference/apis-crypto-architecture-kit/capi-crypto-asym-key-h.md#oh_cryptoasymkeygenerator_generate) to generate an asymmetric key pair (**keyPair**) of the RSA2048 type with two prime numbers. The **keyPair** object includes a public key (**PubKey**) and a private key (**PriKey**).
13
14   For details about how to generate an RSA asymmetric key pair, see the following example. To learn more, see [RSA](crypto-asym-key-generation-conversion-spec.md#rsa) and [Randomly Generating an Asymmetric Key Pair (C/C++)](crypto-generate-asym-key-pair-randomly-ndk.md). There may be differences between the input parameters in the reference documents and those in the following example.
15
162. Call [OH_CryptoPrivKeyEncodingParams_Create](../../reference/apis-crypto-architecture-kit/capi-crypto-asym-key-h.md#oh_cryptoprivkeyencodingparams_create) to create a parameter object (**params**), and call [OH_CryptoPrivKeyEncodingParams_SetParam](../../reference/apis-crypto-architecture-kit/capi-crypto-asym-key-h.md#oh_cryptoprivkeyencodingparams_setparam) to set the encryption algorithm and password.
17
183. Call [OH_CryptoPrivKey_Encode](../../reference/apis-crypto-architecture-kit/capi-crypto-asym-key-h.md#oh_cryptoprivkey_encode) and pass **CRYPTO_PEM/CRYPTO_DER**, **PKCS1/PCKS8**, and the parameter object (**params**) to generate the encoded private key string.
19
20**Decoding**
21
221. Call [OH_CryptoAsymKeyGenerator_Create](../../reference/apis-crypto-architecture-kit/capi-crypto-asym-key-h.md#oh_cryptoasymkeygenerator_create) to generate an RSA asymmetric key generator (**keyGen**).
23
24   For details about how to generate an RSA asymmetric key pair, see the following example and [RSA](crypto-asym-key-generation-conversion-spec.md#rsa).
25
262. Call [OH_CryptoAsymKeyGenerator_SetPassword] to pass the encoded private key string and encoding password.
27
283. Call [OH_CryptoAsymKeyGenerator_Convert] and pass the **CRYPTO_PEM** parameter and the encoded private key string. The RSA key pair is returned.
29
30- Encoding example:
31```C++
32#include "CryptoArchitectureKit/crypto_architecture_kit.h"
33
34static OH_Crypto_ErrCode doTestPriKeyPkcs1Encoded()
35{
36    OH_CryptoAsymKeyGenerator *keyGen = nullptr;
37    OH_Crypto_ErrCode ret = OH_CryptoAsymKeyGenerator_Create("RSA2048", &keyGen);
38    if (ret != CRYPTO_SUCCESS) {
39        return ret;
40    }
41    OH_CryptoKeyPair *keyPair = nullptr;
42    ret = OH_CryptoAsymKeyGenerator_Generate(keyGen, &keyPair);
43    if (ret != CRYPTO_SUCCESS) {
44        OH_CryptoAsymKeyGenerator_Destroy(keyGen);
45        return ret;
46    }
47
48    OH_CryptoPrivKey *privKey = OH_CryptoKeyPair_GetPrivKey(keyPair);
49    if (privKey == nullptr) {
50        OH_CryptoKeyPair_Destroy(keyPair);
51        OH_CryptoAsymKeyGenerator_Destroy(keyGen);
52        return CRYPTO_OPERTION_ERROR;
53    }
54    OH_CryptoPrivKeyEncodingParams *params = nullptr;
55    ret = OH_CryptoPrivKeyEncodingParams_Create(&params);
56    if (ret != CRYPTO_SUCCESS) {
57        OH_CryptoKeyPair_Destroy(keyPair);
58        OH_CryptoAsymKeyGenerator_Destroy(keyGen);
59        return ret;
60    }
61
62    Crypto_DataBlob password = {(uint8_t *)"1234567890", 10};
63    Crypto_DataBlob cipher = {(uint8_t *)"AES-128-CBC", 11};
64    ret = OH_CryptoPrivKeyEncodingParams_SetParam(params, CRYPTO_PRIVATE_KEY_ENCODING_PASSWORD_STR, &password);
65    if (ret != CRYPTO_SUCCESS) {
66        OH_CryptoPrivKeyEncodingParams_Destroy(params);
67        OH_CryptoKeyPair_Destroy(keyPair);
68        OH_CryptoAsymKeyGenerator_Destroy(keyGen);
69        return ret;
70    }
71    ret = OH_CryptoPrivKeyEncodingParams_SetParam(params, CRYPTO_PRIVATE_KEY_ENCODING_SYMMETRIC_CIPHER_STR, &cipher);
72    if (ret != CRYPTO_SUCCESS) {
73        OH_CryptoPrivKeyEncodingParams_Destroy(params);
74        OH_CryptoKeyPair_Destroy(keyPair);
75        OH_CryptoAsymKeyGenerator_Destroy(keyGen);
76        return ret;
77    }
78
79    Crypto_DataBlob pemData = {0};
80    ret = OH_CryptoPrivKey_Encode(privKey, CRYPTO_PEM, "PKCS1", params, &pemData);
81    if (ret != CRYPTO_SUCCESS) {
82        OH_CryptoPrivKeyEncodingParams_Destroy(params);
83        OH_CryptoKeyPair_Destroy(keyPair);
84        OH_CryptoAsymKeyGenerator_Destroy(keyGen);
85        return ret;
86    }
87    OH_Crypto_FreeDataBlob(&pemData);
88    OH_CryptoPrivKeyEncodingParams_Destroy(params);
89    OH_CryptoKeyPair_Destroy(keyPair);
90    OH_CryptoAsymKeyGenerator_Destroy(keyGen);
91    return ret;
92}
93```
94
95- Decoding example:
96```C++
97#include "CryptoArchitectureKit/crypto_architecture_kit.h"
98#include <string>
99
100static OH_Crypto_ErrCode doTestConvertPemKeyByPromise()
101{
102    std::string priKeyPkcs1EncodingStr = "-----BEGIN RSA PRIVATE KEY-----\n"
103                                         "Proc-Type: 4,ENCRYPTED\n"
104                                         "DEK-Info: AES-128-CBC,815A066131BF05CF87CE610A59CC69AE\n\n"
105                                         "7Jd0vmOmYGFZ2yRY8fqRl3+6rQlFtNcMILvcb5KWHDSrxA0ULmJE7CW0DSRikHoA\n"
106                                         "t0KgafhYXeQXh0dRy9lvVRAFSLHCLJVjchx90V7ZSivBFEq7+iTozVp4AlbgYsJP\n"
107                                         "vx/1sfZD2WAcyMJ7IDmJyft7xnpVSXsyWGTT4f3eaHJIh1dqjwrso7ucAW0FK6rp\n"
108                                         "/TONyOoXNfXtRbVtxNyCWBxt4HCSclDZFvS9y8fz9ZwmCUV7jei/YdzyQI2wnE13\n"
109                                         "W8cKlpzRFL6BWi8XPrUtAw5MWeHBAPUgPWMfcmiaeyi5BJFhQCrHLi+Gj4EEJvp7\n"
110                                         "mP5cbnQAx6+paV5z9m71SKrI/WSc4ixsYYdVmlL/qwAK9YliFfoPl030YJWW6rFf\n"
111                                         "T7J9BUlHGUJ0RB2lURNNLakM+UZRkeE9TByzCzgTxuQtyv5Lwsh2mAk3ia5x0kUO\n"
112                                         "LHg3Eoabhdh+YZA5hHaxnpF7VjspB78E0F9Btq+A41rSJ6zDOdToHey4MJ2nxdey\n"
113                                         "Z3bi81TZ6Fp4IuROrvZ2B/Xl3uNKR7n+AHRKnaAO87ywzyltvjwSh2y3xhJueiRs\n"
114                                         "BiYkyL3/fnocD3pexTdN6h3JgQGgO5GV8zw/NrxA85mw8o9im0HreuFObmNj36T9\n"
115                                         "k5N+R/QIXW83cIQOLaWK1ThYcluytf0tDRiMoKqULiaA6HvDMigExLxuhCtnoF8I\n"
116                                         "iOLN1cPdEVQjzwDHLqXP2DbWW1z9iRepLZlEm1hLRLEmOrTGKezYupVv306SSa6J\n"
117                                         "OA55lAeXMbyjFaYCr54HWrpt4NwNBX1efMUURc+1LcHpzFrBTTLbfjIyq6as49pH\n"
118                                         "-----END RSA PRIVATE KEY-----\n";
119
120    OH_CryptoAsymKeyGenerator *keyGen = nullptr;
121    OH_Crypto_ErrCode ret = OH_CryptoAsymKeyGenerator_Create("RSA2048", &keyGen);
122    if (ret != CRYPTO_SUCCESS) {
123        return ret;
124    }
125
126    OH_CryptoKeyPair *dupKeyPair = nullptr;
127    Crypto_DataBlob priKeyPkcs1EncodingData = {};
128    priKeyPkcs1EncodingData.data = reinterpret_cast<uint8_t *>(const_cast<char *>(priKeyPkcs1EncodingStr.c_str()));
129    priKeyPkcs1EncodingData.len = strlen(priKeyPkcs1EncodingStr.c_str());
130    std::string password = "123456";
131    ret = OH_CryptoAsymKeyGenerator_SetPassword(keyGen, reinterpret_cast<const unsigned char *>(password.c_str()),
132        password.size());
133    if (ret != CRYPTO_SUCCESS) {
134        OH_CryptoAsymKeyGenerator_Destroy(keyGen);
135        return ret;
136    }
137    ret = OH_CryptoAsymKeyGenerator_Convert(keyGen, CRYPTO_PEM, nullptr, &priKeyPkcs1EncodingData, &dupKeyPair);
138    if (ret != CRYPTO_SUCCESS) {
139        OH_CryptoAsymKeyGenerator_Destroy(keyGen);
140        return ret;
141    }
142    OH_CryptoKeyPair_Destroy(dupKeyPair);
143    OH_CryptoAsymKeyGenerator_Destroy(keyGen);
144    return ret;
145}
146```
147